Climate control systems have long been provided in vehicles to improve driver comfort during driving. A driver may select a desired cabin temperature via a control panel. The climate control system heats and/or cools air in the cabin to provide the driver selected desired cabin temperature. In one example, cabin air is heated by passing air over a heat exchanger that contains heated engine coolant and distributing the air in the vehicle cabin. Cabin air may also be cooled by passing air over an evaporator and directing cooled air to the cabin. Air around the evaporator is cooled when liquid coolant changes to a gas in the evaporator thereby absorbing heat from the surrounding air. The gas in the evaporator is then compressed to a liquid and heat in the liquid is released to an area outside the cabin.
The air that is cooled or heated may be drawn from outside of the vehicle or from inside the vehicle. Air from outside the cabin is often directed to the evaporator or the heat exchanger because the outside air replaces stale cabin air. Nevertheless, during very warm ambient temperature days, it may be desirable to recirculate air within the cabin to provide lower cabin temperatures as compared with when air from outside the cabin is circulated in the cabin.
Climate control systems improve occupant comfort but they may also reduce vehicle performance since a portion of output from an engine and/or motor is used to operate the climate control system. As a result, vehicle performance may be reduced when a climate control system is activated. One way to mitigate a reduction in vehicle performance due to a climate control system is to deactivate or reduce output from the climate control system during high load conditions. For example, when a driver demand a high level of torque from a motor or engine, an air conditioner compressor may be temporarily deactivated in response to the high level of torque requested by the driver. However, cabin comfort may be reduced during high load conditions since air conditioner output is reduced. Thus, there may be competing requirements between increasing vehicle wheel torque and providing comfort for a driver in the vehicle cabin.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for controlling a vehicle climate system, comprising: adjusting an air mixing valve state and a compressor in response to a energy conversion device load greater than a threshold.
By adjusting an air mixing valve and a compressor in response to a energy conversion device load greater than a threshold, it may be possible to reduce a load on a climate control system and extend the time that cabin air can be cooled. For example, during a humid day, 40% of an air conditioner load may result from dehumidifying air passing over an evaporator rather than cooling the air. Consequently, the cooling capability of an evaporator may be extended when the air mixing valve is adjusted to recirculate a higher percentage of air in a vehicle cabin.
In one example, an air mixing door in the vehicle heating ventilation and air conditioning (HVAC) system is closed when an engine torque production request is greater than a threshold so that a percentage of air circulating in a vehicle cabin and over an evaporator is increased. In other words, a higher percentage of air that is already in the cabin is circulated over an evaporator. In another example, the air mixing door is closed when engine intake manifold vacuum is greater than a threshold so that a percentage of air circulating in a vehicle cabin and over an evaporator is increased. In these ways, reduction in air conditioner compressor output may be made less noticeable to a driver. Without such operation reduction in air conditioner compressor output may be readily sensed by cabin occupants as an increase in temperature and humidity.
The present description may provide several advantages. Specifically, the approach may improve air conditioning system response. In addition, the approach may simplify system design since a complex system model may be unnecessary. Further, the approach may reduce the possibility of introducing phase oscillations that may be caused by long system delays.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.